1. Field of the Invention
The present invention relates to a material sheet adapted for use in forming a sintered layer on a surface of a metal substrate. More particularly, the present invention relates to a powder sheet which can be sintered under a relatively low temperature.
2. Description of Prior Art
It has been known to provide an alloy powder sheet which is used for forming a sintered layer on a metal surface. Such a powder sheet has been generally produced by kneading alloy powders with a synthetic resin and rolling the mixture into a sheet form. The sheet is fitted to a surface of a metal substrate and thereafter heated to a sintering temperature to have the alloy powders sintered to thereby form a sintered alloy layer on the surface of the metal substrate. For example, the Japanese patent application No. 50-9398 filed on Jan. 21, 1975 and disclosed for public inspection under the disclosure number 51-83834 proposes to provide an alloy powder sheet made of powders of self-melting alloy and thermoplastic acryl resin, attach the sheet to a metal substrate by wetting the sheet by a solvent such as toluene, and heat under atmosphere to a melting temperature.
Japanese patent publication 55-21802 proposes to provide a thin tape by kneading powders of TiC type alloy with a synthetic resin and sinter the tape under a pressed condition to form a sintered sheet which is then attached to a mold of a substrate. By molding the substrate in the mold having the sintered tape attached thereto, it is possible to provide a sintered alloy layer on the substrate.
According to the process proposed by the Japanese patent application No. 50-9398, the resin in the alloy powder sheet functions to make the sheet adhere to the metal substrate as long as the temperature is between 200.degree. and 300.degree. C. It has been found, however, that under a further high temperature the resin is burnt or dissipated by heat so that the adhesive power of the alloy sheet to the substrate is no longer maintained. This property produces problems when the alloy sheet is to be attached to a slanted surface, a curved surface or a downwardly faced surface because the sheet cannot be held in position during the sintering process. The process as proposed by the Japanese patent publication 55-21802 may not have the above problems, however, it requires increased process steps to that it is disadvantageous in terms of the manufacturing cost.
Japanese patent publication 53-19540 proposes to use a sheet containing alloy powders of a high melting point superimposed on a second sheet containing alloy powders of a low melting point for sintering on a metal substrate. It should however be noted that in the proposed process it is required for sintering to have the alloy powders molten to some extent so that a high sintering temperature, usually higher than 1000.degree. C., is generally required. Such high sintering temperature causes distortions in the metal substrate. Further, the process is difficult to apply to a metal substrate of a relatiely low melting point.